<article id="wikiArticle">
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<p><strong><code>Math.acosh()</code></strong><code>返回一个数字的反双曲余弦值，即：</code></p>
<p><math display="block"><semantics><mrow><mo>∀</mo><mi>x</mi><mo>≥</mo><mn>1</mn><mo>,</mo><mstyle mathvariant="monospace"><mrow><mo lspace="0em" rspace="thinmathspace">Math.acosh</mo><mo stretchy="false">(</mo><mi>x</mi><mo stretchy="false">)</mo></mrow></mstyle><mo>=</mo><mo lspace="0em" rspace="thinmathspace">arcosh</mo><mo stretchy="false">(</mo><mi>x</mi><mo stretchy="false">)</mo><mo>=</mo><mtext> the unique </mtext><mspace width="thickmathspace"></mspace><mi>y</mi><mo>≥</mo><mn>0</mn><mspace width="thickmathspace"></mspace><mtext>such that</mtext><mspace width="thickmathspace"></mspace><mo lspace="0em" rspace="0em">cosh</mo><mo stretchy="false">(</mo><mi>y</mi><mo stretchy="false">)</mo><mo>=</mo><mi>x</mi></mrow><annotation encoding="TeX">\forall x \geq 1, \mathtt{\operatorname{Math.acosh}(x)} = \operatorname{arcosh}(x) = \text{ the unique } \; y \geq 0 \; \text{such that} \; \cosh(y) = x</annotation></semantics></math></p>
<h2 id="语法">语法</h2>
<pre><code class="language-javascript"><code>Math.acosh(<var>x</var>)</code></code></pre>
<h3 id="参数">参数</h3>
<dl>
<dt><code>x</code></dt>
<dd>一个数字。</dd>
</dl>
<h3 id="返回值">返回值</h3>
<p>返回指定参数的反双曲余弦值，如果指定的参数小于 1 则返回<a href="Reference/Global_Objects/NaN" title="全局属性 NaN 的值表示不是一个数字（Not-A-Number）。"><code>NaN</code></a>。</p>
<h2 id="描述">描述</h2>
<p>因为<code>acosh()</code>是Math对象的静态方法，所以你应该像这样使用它：<code>Math.acosh()</code>, 而不是作为你创建的Math实例的属性（Math不是构造函数）。</p>
<h2 id="示例">示例</h2>
<h3 id="使用_Math.acosh()">使用 <code>Math.acosh()</code></h3>
<pre><code  class="language-javascript">Math.acosh(-1);  // NaN
Math.acosh(0);   // NaN
Math.acosh(0.5); // NaN
Math.acosh(1);   // 0
Math.acosh(2);   // 1.3169578969248166
</code></pre>
<p>当参数小于1时， <code>Math.acosh()</code>将返回 <a href="Reference/Global_Objects/NaN" title="全局属性 NaN 的值表示不是一个数字（Not-A-Number）。"><code>NaN</code></a>。</p>
<h2 id="替代方案">替代方案</h2>
<p>当 <math><semantics><mrow><mi>x</mi><mo>≥</mo><mn>1</mn></mrow></semantics></math> 时，都有 <math><semantics><mrow><mo lspace="0em" rspace="thinmathspace">arcosh</mo><mo stretchy="false">(</mo><mi>x</mi><mo stretchy="false">)</mo><mo>=</mo><mo lspace="0em" rspace="0em">ln</mo><mrow><mo>(</mo><mrow><mi>x</mi><mo>+</mo><msqrt><mrow><msup><mi>x</mi><mn>2</mn></msup><mo>-</mo><mn>1</mn></mrow></msqrt></mrow><mo>)</mo></mrow></mrow><annotation encoding="TeX">\operatorname {arcosh} (x) = \ln \left(x + \sqrt{x^{2} - 1} \right)</annotation></semantics></math> ，因此我们可以使用以下函数来模仿Math.acosh()：</p>
<pre><code  class="language-javascript">Math.acosh = Math.acosh || function(x) {
  return Math.log(x + Math.sqrt(x * x - 1));
};
</code></pre>
<h2 id="规范">规范</h2>
<table class="standard-table">
<tbody>
<tr>
<th scope="col">版本</th>
<th scope="col">状态</th>
<th scope="col">注释</th>
</tr>
<tr>
<td><a class="external" href="https://www.ecma-international.org/ecma-262/6.0/#sec-math.acosh" hreflang="en" lang="en" rel="noopener">ECMAScript 2015 (6th Edition, ECMA-262)<br/><small lang="zh-CN">Math.acosh</small></a></td>
<td><span class="spec-Standard">Standard</span></td>
<td>Initial definition.</td>
</tr>
<tr>
<td><a class="external" href="https://tc39.github.io/ecma262/#sec-math.acosh" hreflang="en" lang="en" rel="noopener">ECMAScript Latest Draft (ECMA-262)<br/><small lang="zh-CN">Math.acosh</small></a></td>
<td><span class="spec-Draft">Draft</span></td>
<td> </td>
</tr>
</tbody>
</table>
<h2 id="浏览器兼容性">浏览器兼容性</h2>
<div><div class="blockIndicator warning"><strong><a class="external" href="https://github.com/mdn/browser-compat-data" rel="noopener">We're converting our compatibility data into a machine-readable JSON format</a></strong>.
            This compatibility table still uses the old format,
            because we haven't yet converted the data it contains.
            <strong><a class="new" href="/zh-CN/docs/MDN/Contribute/Structures/Compatibility_tables" rel="nofollow">Find out how you can help!</a></strong></div>
<div class="htab">
<a id="AutoCompatibilityTable" name="AutoCompatibilityTable"></a>
<ul>
<li class="selected"><a>Desktop</a></li>
<li><a>Mobile</a></li>
</ul>
</div></div>
<div id="compat-desktop">
<table class="compat-table">
<tbody>
<tr>
<th>Feature</th>
<th>Chrome</th>
<th>Firefox (Gecko)</th>
<th>Internet Explorer</th>
<th>Opera</th>
<th>Safari</th>
</tr>
<tr>
<td>Basic support</td>
<td>38</td>
<td><a href="/en-US/Firefox/Releases/25" title="Released on 2013-10-29.">25</a> (25)</td>
<td><span style="color: #f00;">未实现</span></td>
<td>25</td>
<td>7.1</td>
</tr>
</tbody>
</table>
</div>
<div id="compat-mobile">
<table class="compat-table">
<tbody>
<tr>
<th>Feature</th>
<th>Android</th>
<th>Chrome for Android</th>
<th>Firefox Mobile (Gecko)</th>
<th>IE Mobile</th>
<th>Opera Mobile</th>
<th>Safari Mobile</th>
</tr>
<tr>
<td>Basic support</td>
<td><span style="color: #f00;">未实现</span></td>
<td><span style="color: #f00;">未实现</span></td>
<td>25.0 (25)</td>
<td><span style="color: #f00;">未实现</span></td>
<td><span style="color: #f00;">未实现</span></td>
<td>8</td>
</tr>
</tbody>
</table>
</div>
<h2 id="相关链接">相关链接</h2>
<ul>
<li><a href="Reference/Global_Objects/Math/asinh" title="Math.asinh() 函数返回给定数字的反双曲正弦值, 即："><code>Math.asinh()</code></a></li>
<li><a href="Reference/Global_Objects/Math/atanh" title="Math.atanh() 函数返回一个数值反双曲正切值, 即："><code>Math.atanh()</code></a></li>
<li><a href="Reference/Global_Objects/Math/cosh" title="Math.cosh() 函数返回数值的双曲余弦函数, 可用 constant e 表示:"><code>Math.cosh()</code></a></li>
<li><a href="Reference/Global_Objects/Math/sinh" title="Math.sinh() 函数返回一个数字(单位为角度)的双曲正弦值."><code>Math.sinh()</code></a></li>
<li><a href="Reference/Global_Objects/Math/tanh" title="Math.tanh() 函数将会返回一个数的双曲正切函数值，计算如下:"><code>Math.tanh()</code></a></li>
</ul>
</article>